It is there to do exactly what he says it does. With the jumper it limits the drive to SATA 1.5 Gb/s, without the jumper it runs at SATA 3.0 Gb/s. It is there to make the drive compatible with the few SATA controllers that don't like SATA 3.0 Gb/s.

However, there is no speed difference between SATA 1.5 Gb/s and SATA 3.0 Gb/s. SATA 3.0 Gb/s is just a big marketing gimmick. 7200 and 10000RPM drives simply aren't fast enough to use all the bandwidth SATA 1.5 G/bs provides, so SATA 3.0 Gb/s is useless.

My hard drive is the seagate 250 MB. HD tach reports burst transfer rates above the bandwidth of SATA150. So while you may or may not notice any real world difference you should still remove the jumper as long as you don't face any compatibility issues.

I just bought the same drive. I am putting vista on it however.
I remember reading a review that you had to put a floppy disk w/ drivers for the HDD in for windows to recognize it. I would try to google it or got to seagate's website.